Revision: Biomolecules Chemistry HSC Science Class 12 Tamil Nadu Board of Secondary Education

Carbohydrates are optically active polyhydroxy aldehydes or polyhydroxy ketones or compounds that can be hydrolysed to polyhydroxy aldehydes or polyhydroxy ketones.

The sugars that reduce the Tollen's reagent and Fehling's solution are called reducing sugars.

Carbohydrates may be defined as optically active polyhydroxy aldehydes or ketones or compounds which produce such units on hydrolysis, such as cellulose, glycogen, starch, etc.

Carbohydrates that are crystalline solids, sweet in taste and soluble in water are called sugars.

Carbohydrates that are amorphous solids, tasteless and insoluble in water are catled non-sugars.

Enzymes are biological catalysts that speed up chemical reactions in living cells without being consumed in the process.

Bifunctional organic compounds containing a carboxylic and an amino group either at the same carbon atom or at nearby carbon atoms are called amino acids.

Proteins are complex polyamides formed from amino acids. They are essential for the proper growth and maintenance of the body. They have many peptide (-CO–NH )bonds.

Chemically, proteins are polyamides, which are high molecular weight polymers of the monomer units called \[\alpha\]-amino acids.

α-Amino acids are carboxylic acids having an amino (–NH₂) group bonded to the α-carbon, that is, the carbon next to the carboxyl (–COOH) group.

The bond that connects α-amino acids to each other is called a peptide bond.

Chemically proteins are polyamides which are high molecular weight polymers of the monomer units, i.e., α-amino acids. OR It can also be defined as proteins are the biopolymers of a large number of α-amino acids and they are naturally occurring polymeric nitrogenous organic compounds containing 16% nitrogen and peptide linkages (-CO-NH-)

Hormones are chemical messengers created by the endocrine glands and transported through the bloodstream to govern body functions such as development, metabolism, reproduction and mood by interacting with specific target cells.

• Carbohydrates are organic biomolecules made of C, H and O, usually fitting the general formula Cx(H₂O)y and existing as aldoses or ketoses.
• They are classified into monosaccharides, disaccharides and polysaccharides; monosaccharides cannot be hydrolysed further, disaccharides are formed by two monosaccharides via glycosidic bonds, and polysaccharides are long polymers.
• Some sugars like digitoxose (C₆H₁₂O₄) and rhamnose (C₆H₁₂O₅) do not obey the typical Cx(H₂O)y formula.
• All monosaccharides are reducing sugars because they possess a free aldehyde or ketone group.
• Cellulose is a linear polymer of β‑D‑glucose, unlike starch and glycogen, which are polymers of α‑glucose and show branching.
• Biologically, carbohydrates supply energy for metabolism; glucose is the main substrate for ATP synthesis, and lactose provides energy to infants.
• Polysaccharides such as starch and glycogen act as storage products and also contribute to structural components of cell membranes and cell walls.

• Proteins are polymers of amino acids (polypeptides) in which amino acids are linked by peptide bonds.
• There are 20 types of amino acids, so proteins are heteropolymers (not homopolymers).
• Amino acids are of two types: essential (must be obtained from diet) and non-essential (can be synthesised in the body).
• Proteins are high molecular weight biomolecules (polyamides) made of α-amino acids with a general structure R-CH(NH₂)-COOH.
• Proteins perform various functions such as enzymatic activity, transport, hormonal regulation, immunity, and sensory reception.
• Proteins are of two main types: fibrous proteins (insoluble, structural, e.g., keratin) and globular proteins (soluble, functional, e.g., enzymes, insulin).
• Collagen is the most abundant protein in animals, while RuBisCO is the most abundant enzyme in the biosphere.

• Lipids are esters of fatty acids with a hydrogen-to-oxygen ratio greater than 2:1.
• They are classified into simple lipids (fats and waxes), compound lipids (phospholipids, glycolipids, lipoproteins) and sterols (derived lipids).
• Simple lipids are esters of fatty acids with various alcohols, while compound lipids typically contain 1 glycerol, 2 fatty acids and either 1 phosphate group (phospholipid) or 1 simple sugar (glycolipid).
• Glycolipids, also called cerebrosides, are abundant in the myelin sheath of nerve cells.
• In plants, sterols occur as phytosterols; the yam plant (Dioscorea) yields the sterol diosgenin, used to manufacture birth‑control pills.

• Chemical coordination is the process by which cells and organisms communicate using chemical signals.
• There are four types of chemical signaling: autocrine, paracrine, endocrine, and pheromones.
• Hormones are chemical messengers that regulate various body functions.
• Hormones are classified based on their chemical nature into amines, peptide/protein hormones, steroid hormones, fatty acid derivatives, and gases.
• Examples include epinephrine and thyroxine (amines), insulin and growth hormone (proteins), estrogen and testosterone (steroids), prostaglandins (fatty acids), and nitric oxide (gas).